The present invention generally relates to syringes for injecting liquid medications from prefilled cartridges, and more particularly to a syringe having a buffering agent delivery system for reducing the acidity of anesthetic.
Local anesthetic is frequently used to numb tissue in a patient's mouth to reduce pain and discomfort a patient may feel during a dental procedure. Conventionally, a reusable syringe assembly is used to inject the anesthetic or medicine from a cartridge or carpule. The cartridge is a glass cylinder containing a local anesthetic and other ingredients. A diaphragm at one end of the cylinder is held in place by an aluminum band. The opposite end of the cylinder has a moveable piston or stopper. The syringe assembly includes a barrel for receiving the cartridge, a plunger rod slidably received in a proximal end of the barrel for actuating the cartridge, an access needle at a distal end of the barrel for puncturing the diaphragm, and a delivery needle connected to the access needle for delivering anesthetic to the patient. In some cases, the plunger rod includes a harpoon for engaging the piston.
Typically, the diaphragm of the cartridge is swabbed with alcohol before being loaded into a pre-sterilized syringe. As the cartridge is loaded into the syringe, the access needle extending proximally from the distal end of the barrel pierces the cartridge diaphragm so the anesthetic in the cartridge can be dispensed. Once the cartridge is in place, the plunger rod of the syringe pushes the piston of the cartridge toward the diaphragm, forcing anesthetic through the access needle, into the delivery needle, and ultimately into the patient.
Frequently, a topical anesthetic is used to reduce pain caused by the entry of the needle into the tissue and the delivery of the medicine. Among the properties that make anesthetic delivery painful is its acidity. Local anesthetic solutions containing vasopressors (e.g., epinephrine) are intentionally manufactured with lower pH (3-4 pH) to slow the oxidation of the vasopressor prolonging its effectiveness and thereby extending the shelf life of the drug. Thus, there is a need for a device that delivers effective anesthetic having a reduced acidity, without affecting the shelf life of the drug.
The present invention relates to a dental syringe for dispensing anesthetic from a cartridge having an interior wall defining a hollow interior sized and shaped for receiving a dose of anesthetic, and a piston. The syringe comprises a tubular plunger slidably received in the hollow interior of the tubular barrel. The plunger has a hollow interior extending between a distal end shaped for engaging the piston and an open proximal end opposite the distal end. In addition, the syringe includes a plunger rod slidably received in the hollow interior of the tubular plunger. The rod has a sharp distal end adapted to penetrate the seal, a proximal end, and a length extending between the distal end and the proximal end sized so that a delivery portion of the rod extends through the piston into the cartridge when the rod is driven through the piston. The delivery portion includes a recess for receiving a buffering agent to reduce an acidity of the dose of anesthetic.